The present invention relates to cooking ovens, and more particularly to a self-cleaning cooking oven which is capable of automatically eliminating food soils accumulated on its walls by a pyrolytic process at a high temperature.
Generally known as dislosed in U.S Pat. Nos. 3,428,434, 3,536,457 and 4,292,501 are cooking ovens such as electric ovens, gas ovens and convection microwave ovens which can not only be used for normal cookings but also can pyrolytically eliminate food soils attached to its walls during the normal cookings. The pyrolytic elimination can be effected with two processes: one process being to pyrolytically degrade food soils in a cooking chamber maintained at a high cleaning temperature more than 440.degree. C. for one to four hours so as to generate smoke, odors and gases and the other process being to oxidize the smoke, odors and gases by an oxidizing catalyst disposed in an exhausting passage when the chamber atmosphere including the smoke, odors and gases is exhausted through the exhausting passage to an ambient atmosphere. Normally, the cleaning time is defined as an interval from the time whereat a heating starts to a time whereat the chamber temperature is cooled to about 300.degree. C. due to heating stop after the chamber temperature is kept to the cleaning temperature, which is generally set to about 470.degree. C., for a predetermined time period and, as disclosed in U.S. Pat. No. 3,121,158, based upon time control using a timer. The cleaning time depends upon the cleaning temperature and the degree of contamination and hence it can be shortened in response to increase in the cleaning temperature and is varied in accordance with the degree of contamination. However, the set cleaning temperature is generally varied by about .+-.30.degree. C., i.e., in a range of 470.+-.30.degree. C., in the practical uses and the cleaning time necessary at the minimum cleaning temperature of 440.degree. C. beomes longer by about 1.5 times than that necessary at the maximum cleaning temperature of 500.degree. C. This shows the fact that difficulty is encountered to accurately determine the cleaning time for elimination of food soils.
In addition, as described above, the cleaning time greatly depends on the amount of food soils in practical uses. In the case of light food soils, the soil-elimination is sufficiently effected with the process wherein the chamber temperature is immediately cooled by stopping the heat supply to the cooking chamber after it arrives at the cleaning temperature. In this case, the cleaning time is to be about one hour (about 1/2 hour for heating-up and about 1/2 hour for cooling-off). On the other hand, in the case of heavy food soils, the chamber temperature is maintained at the cleaning temperature for about three hours. Here, the cleaning time is about four hours (about 1/2 hours for heating-up, about three hours for keeping the cleaning temperature and about 1/2 hours for cooling-off). However, in the practical uses the food contamination in the cooking chamber is frequently in the intermediate state therebetween and in this case it is difficult to accurately determine the cleaning time. This difficulty causes to take an excessive cleaning time for preventing unsufficient soil elimination, thereby consuming energy wastefully.